Microstructure and Properties of Cold Spray Assisted Laser Remelting AlCoxCrFeNiCu High Entropy Alloy Coating
In recent years,the rapid development of material surface treatment technology plays a particularly important role in the progress of modern science and technology,industry and economic development.The surface treatment technology is an important method to improve and repair matrix materials,which can improve the strength,hardness,wear resistance and corrosion resistance of materials.Preparing a layer of alloy coating on the surface of ordinary industrial materials is one of the most effective measures of sur-face treatment,of which advantages are fast and efficient,energy saving,conducive to environmental protection,and plays an irre-placeable role in China sustainable development.The performance of the coating is determined by the material and process method.In order to improve and protect the matrix material,it is very important to select the coating material and design the preparation process.For the selection of materials,so far,the traditional alloy composition is still dominated by one metal element.Human beings have pre-pared different alloys according to this law,adopted different manufacturing processes,and then applied them to different fields,it can be seen from the development of traditional alloys that although adding other alloy elements to the alloy can improve the properties of the alloy,too many alloy elements will lead to the emergence of many compounds,especially brittle intermetallic compounds,which will lead to the deterioration of the properties of the alloy.In addition,it also brings great difficulties to the control of the struc-ture and composition of the material.Therefore,the fewer kinds of alloy elements,the simpler the internal structure of the metal,and the performance of the alloy will become worse.In order to solve these problems,the concept of multi principal component high entro-py alloy is proposed,in which the atomic percentage of each major element is very high.The content of major elements is between 5％～35％,and the content of trace elements is less than 5％.This alloy consists of many elements,each of which has its own characteris-tics.Many studies have shown that various main elements are often disorderly arranged to form a simple crystalline phase.High entropy alloy has the characteristics of high hardness,high temperature resistance and corrosion resistance.The micro nano structure and amor-phous trend of high entropy alloys as cast and tempered also make high entropy alloys have broad application prospects.High entropy alloy has good performance advantages and is the preferred high-performance material for coating preparation.In order to improve the friction resistance of common metal surface,a technical process for preparing AlCoxCrFeNiCu high entropy alloy coating with good per-formance on the surface of common metal material was proposed.Many kinds of main elements led to the high entropy effect in thermo-dynamics,lattice distortion effect in structure,hysteretic diffusion effect in dynamics,cocktail effect in properties and stability in mi-crostructure.These effects endowed multi-element alloys with excellent mechanical properties,such as high strength,good corrosion resistance and excellent wear resistance.These new metal materials were suitable for engineering applications in many fields,such as transportation,national defense or nuclear and biomedical industries,which had aroused high expectations in the industry.Due to the high cost of preparing industrial parts from bulk alloy materials,researchers have prepared multi-element alloys as surface coatings for wear,corrosion and other working conditions,which could not only improve the service life and performance of metal parts,but also reduce the preparation cost AlCoxCrFeNiCu(x=0,0.5,1.0,1.5,2.0)high-entropy alloy coatings with different Co contents were suc-cessfully prepared on the surface of 45#steel by cold spraying assisted laser refusion.The influence of Co content on phase structure,microstructure,hardness and wear resistance of the alloy coating was analyzed by XRD,SEM,EDS,microhardness tester and abra-sive wear testing machine.The results showed that AlCoxCrFeNiCu high entropy alloy coatings were composed of simple body-centered cubic(bcc)and face-centered cubic(fcc)phases.With the increase of Co content,the equiaxed dendrites of AlCoxCrFeNiCu high en-tropy alloy coatings changed from fewer to more and gradually become finer,and the spacing of columnar dendrites increased first and then decreased.Fe,Cr,Co and Ni were enriched in the dendrites,Cu was enriched into dendrites,and Al was evenly distributed throughout the coatings.With the increase of Co content,the hardness of AlCoxCrFeNiCu high entropy alloy coatings increased first and then decreased.When x=1.0,the hardness of AlCo1.0CrFeNiCu high entropy alloy coating reached the maximum value of HV 610.9.Under dry friction conditions,the friction coefficient of AlCoxCrFeNiCu high entropy alloy coatings decreased first and then in-creased.The wear mechanism of AlCoxCrFeNiCu high entropy alloy coatings was abrasive wear and adhesion wear.When x=1.0,the friction coefficient of AlCo1.0CrFeNiCu high entropy alloy coating was 0.346 and the wear rate was 3.62×10-5 mm3·(N·m)-1,which showed good wear resistance.
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